1. Field of the Invention:
This invention relates to a process for wrapping a rotating bale of a backed mineral fiber strip, in the form of a felt roll, with an external closed-face backing, with a protective strip which is applied during winding of the bale; and a device for effecting the process.
2. Description of the Prior Art:
To produce a backed felt roll, mineral fibers with bonding agent are placed on a production line, concentrated to the desired degree and hardened in a tunnel furnace; thereafter, a backing strip, especially one made of aluminum, is applied and bonded to the felt strip so produced. The bonded felt strip so obtained is cut to the required length and the cut sections are wound into bales and enclosed in protective wrapping made of paper or plastic film and thus held together for storage and transportation. Such a backed felt roll is produced and marketed by the applicant under the designation "Rollisol" (registered trade mark) and is used especially for inside roof insulation between the rafters.
To enclose the wound bale in the protective wrapping, segments of the protective wrapping cut to the required length are kept in readiness on a feed conveyor of their own and, in accordance with the advance movement of the felt roll to the winding station, are so fed in that the front end of the protective wrapping is clamped in and carried in the angle between the outside of the already wound felt and the inside of the tailing end of the felt when entering the winding station. Then the completed bale makes another turn and, in doing so, winds the protective wrapping around the outside of the bale starting from the front end until the back end of the protective wrapping overlaps a previously wound middle area of the protective wrapping. Prior to that, the back end has been provided with a quick setting, durably effective adhesive agent and is pressed on during the winding movement, so that the wrapping of the bale with the protective wrapping is continuous and fixed in this position. Then the bale is ejected from the winding station and--in case of a bilaterally protruding shrink film as protective wrapping after pasing through a heating zone for shrinking of the edges as edge protection--stacked and transported.
Carrying the front end of the protective wrapping with the rotating bale by having the front end enter into the last winding of the felt and clamping it in is customary; only by way of example, reference is made to DE-AS No. 12 39 979 and DE-AS No. 14 61 821 or U.S. Pat. No. 3,052,073. This procedure to achieve continuous wrapping over the entire circumference by a protective wrapping automatically as part of the winding process has replaced the former procedure evident, for example, from U.S. Pat. No. 2,681,702, according to which only the felt strip was wound and the last winding of the bale was then held in place and secured by means of a narrow adhesive tape strip; it is obvious that such safeguarding during transport merely by a narrow adhesive tape strip is inadequate for reasons of proneness to damage.
However, a well-known and long-felt problem of continuous wrapping over the entire circumference consists in the fact that the consumption of packaging material in the form of protective wrapping per bale is very high. This has essentially three reasons:
1. To guarantee reliable carrying of the protective wrapping between the end of the felt and the previously wound layer of felt, the overlap of the front end of the protective wrapping with the end of the felt must be relatively wide, as a rule a few decimeters, particularly since the clamping pressure, because of the pliability of the felt, is not that great and takes full effect only sometime after the feed of the front end of the protective wrapping during the further winding movement. Thus the producer of a winding station used in practice cites an estimated overlapping length of 0.5 m between the back end of the felt strip and the front end of the protective wrapping.
2. After one rotation of the bale with the protective wrapping, the latter gets into the area of the end of the felt strip. The felt strip is at least several centimeters thick, as a rule 10 cm or more, so that the trailing end of the felt strip supports the area of the protective wrapping above from the beginning area of the protective wrapping below. Therefore, the protective wrapping must be pulled quite a bit over the trailing end of the felt under tension and under compression of the end of the felt to attain a bonding zone with the preceding winding of the protective wrapping which, on account of the spatial distance, is sufficiently relieved of the spreading forces of the back end of the felt to guarantee a safe bond here as part of the winding process. The distance behind the end of the felt strip needed to join the upper protective wrapping with its previous winding may also amount to a few decimeters.
3. Under severe production conditions, short, slight disturbances of the feed control of the protective wrapping as well as slight changes of adjustments, for example of the advancing mechanism for the protective wrapping, cannot be ruled out. Therefore, it happens time and again that a protective wrapping runs in the winding slightly deviating from the desired feed control. Especially at high production speeds, such slight deviations lead to a possibly considerable variation in the degree of overlapping between the area of the front end of the protective wrapping and the area of the trailing end of the felt. Thus if faulty packaging resulting from fluctuations of the feed time of the protective wrapping occurring during operations to be avoided then, on the one hand, work must be done with such great nominal length of overlap that also in case of a delay of the feed, adequate overlap and carrying are guaranteed and, on the other hand, with such lengths of protective wrapping that, in case of somewhat premature feed, the trailing end of the felt is covered sufficiently widely on the winding by the film strip and tidy bonding at a distance from the trailing end of the felt is guaranteed.
To wrap a bale with an average diameter of 55 cm, and thus a nominal circumference of 173 cm, as a result requires in practice the use of a protective wrapping measuring well over 3 m, in other words, nearly twice the nominal circumference. It is obvious that in mass production even with an inexpensive material for the protective wrapping, such as paper, this comes to a considerable amount; in the case of more expensive material, such as plastic shrink film, this causes a clearly noticeable rise in cost, especially since the protective wrapping in practice must also be used with continuous printing.
It can be seen that a corresponding problem also arises if in place of a backed felt roll another material is to be wound on rolls and wrapped. The material consumption for the protective wrapping because the greater the thicker the trailing end of the winding material and the lower the clamping pressure which the winding material can exert on the front end of the protective wrapping. However, completely apart from the material, is the requirement of a control of the feed time of the protective wrapping, which must be precise as possible, to achieve in each case the desired overlapping with the trailing end of the winding material.
Hence, a need clearly continues to exist for a process for wrapping a rotating bale by which the consumption of material for the protective wrapping can be considerably reduced without abandoning continuous wrapping over the entire circumference.